Fig. 8.

A: Na⁺/Ca²⁺ exchanger (NCX)-dependent rate of intracellular Ca²⁺ concentration ([Ca²⁺]_i) decline after caffeine-induced unloading of the sarcoplasmic reticulum was faster in transgenic α₂ [TG(α₂)] than TG(α₁) or wild-type (Wt) mouse cardiomyocytes. NCX was blocked by 10 mM NiCl₂ (black bars), which lowered the rate of [Ca²⁺]_i decline to about the same level in all three genotypes. *P < 0.05 vs. control (no nickel); #P < 0.05 vs. Wt mice with the same treatment. B and C: intracellular Na⁺ concentration ([Na⁺]_i) was reduced by about 33% in TG(α₁) but not TG(α₂) versus sham cardiomyocytes, both at rest (B) and during 2-Hz stimulation (C). This reduction of [Na⁺]_i did not reach statistical significance, likely because too few myocytes were studied (see footnote 3 in the text). [Data reproduced from Ref. 15 with permission.]